High winds and fast moving cloud mean that there is only periodic direct sunlight, the illumination of the backstone should have begun almost twenty minutes ago but finally at 7.35am the wait is over and its time to go inside the chamber.

Hazy sunshine streams down the short passage, the beam hitting the backstone is now shaped by the orthostats and lintel in the passage and also the sill stone in the foreground. This arrangement creates a roughly square beam of light that first frames a circular design commonly called a 'sun symbol' on the upper left of the backstone in the rear chamber before widening and elongating to illuminate the whole stone before shrinking again to frame a very similar design on the lower left hand side of the same stone.

A narrow beam of light signals the ending of the illumination of the heavily carved backstone, with the unpredictable weather at the time of the equinox in September and March, this could be the last time the sun shines directly onto the backstone for many months, if not years. More often than not, the trek up the mountain in the dark is not rewarded by this fascinating show of engineering and astronomy.

Here you can see just how strong the projected beam is in the chamber. At this point the beam is entirely cast onto stone 6 in the main chamber, it will reach the small circular carving just visible to the top right of the sunbeam before stopping and shrinking from right to left until the chamber returns to gloomy darkness.